Trace Chemicals Not Always Harmful
We frequently read media reports about medical tests detecting trace levels of environmental chemicals--DDT, PCBs, lead or other toxins--in human blood, tissue, or even breast milk. The implication of such reports is that the mere presence in the body of such chemicals, even in minute quantities, poses a hazard to health or suggests some underlying disease or adverse condition. That implication is a false one.
The detection of trace levels of a chemical in a human body simply provides evidence of that body’s having been exposed to that chemical. The mere presence of such chemical traces generally does not indicate any adverse health consequences at all.
A new ACSH report, “Traces of Environmental Chemicals in the Human Body: Are They a Risk to Health,” examines the implications for human health of trace chemicals in the body.
The report notes that all living organisms are continually exposed to foreign chemicals, also known as “xenobiotics.” These chemicals include substances that are natural (e.g., toxins produced by molds, plants, and animals) and substances that are man-made (e.g., drugs, industrial chemicals, pesticides, and pollutants).
Human tissues and body fluids may contain many different xenobiotics, most of them present at trace levels and some of them essential to life. Trace chemicals in the body can be detected through the study of “biomarkers” in the blood, in other body fluids, or in tissues.
Biomarkers--short for “biological markers”--may be defined as any measurable alterations in cells or biochemical processes. Biomarkers are useful primarily as signals of exposure to a given substance, rather than as direct indicators of any harmful effect the substance may have caused.
When studied in conjunction with other toxicological or clinical signs, biomarkers can help clinicians diagnose or predict the development of diseases that might be related to patients’ exposures to foreign substances. But improvements in analytical methods now make possible the detection in the body of increasingly smaller traces of xenobiotic substances.
The relationships between biomarkers, exposure, and the risk of adverse health effects thus have become less certain.
The presence in the body of a trace chemical generally signifies occupational or lifestyle-related exposure to that substance. Such a presence alone should not be over interpreted as necessarily injurious to health.
No Risk to Health
For the vast majority of exogenous chemicals (chemicals originating outside the body), there is no evidence to suggest that trace concentrations in the body present a risk to human health.
The presence of trace levels of environmental chemicals in hair, body fluids, and tissues is a reflection of our daily exposure to many such chemicals. These substances include natural chemicals, pharmaceutical agents, and environmental pollutants. Many of these substances are eliminated naturally from the body in the course of normal metabolism and excretion.
Some biomarkers can be found through routine clinical tests using blood and urine samples. Biomarkers thus found can be considered as useful pieces of evidence among the many often utilized in making clinical evaluations.
Occupational physicians, clinicians, and other scientists use biomarkers as tools to assist their evaluations of human health. The use of biomarkers alone to determine health risks is not generally accepted, however, because of biomarkers’ limited ability to aid in the diagnosis of adverse health effects or disease.
The health implications of finding trace amounts of certain substances in human tissues are certainly valid causes for concern. An important principle of toxicology, however, is that “the dose makes the poison.” Toxicity or other adverse effects of a given exogenous substance in the body depend on how much of that substance the body has been exposed to. The simple presence of a chemical in the body should not necessarily be equated with toxicity.
Every day of our lives, every one of us is exposed to a multitude of potentially toxic and carcinogenic substances, both natural and synthetic. But we humans are equipped with a set of biological defense mechanisms that can successfully manage our exposures to many foreign substances. Thus, we need not feel undue anxiety when faced with positive results after a blood-screening analysis.
Such an analysis provides a snapshot in time, both of a person’s lifestyle and of that person’s relationship to his or her environment. The presence of certain biomarkers may indeed indicate a high-exposure situation and may point to a need for further clinical evaluation. The following key questions can provide a context in which to interpret the presence of trace chemicals in the body.
- What is the concentration in the body of the substance of concern as compared with typical or expected ranges for that substance?
- Has the chemical ever been associated with a particular health hazard?
- Are there predisposing exposure factors (occupational or environmental factors, for example) that might contribute to a heightened body burden or blood concentration of the substance in a particular individual?
- Are there factors of increased susceptibility--such as compromised health status, age, or genetic predisposition--in a particular individual (in a young child with high blood lead levels, for example)?
- Are there other clinical or toxicological correlates (clinical chemistry values, actual pathology, clinical observations) that suggest adverse health effects resulting from exposure?
The last few decades have seen notable decreases in the release of chemicals into the air, the water, and the land. As a result, our environment has improved with respect to the quantities of such chemicals present in it. With this trend continuing, the levels of trace chemicals in our bodies should continue to decline as well.
The trace chemicals in our blood and bodies often serve as biomarkers of background environmental exposure, but no data or evidence exists for most chemicals that would suggest an increased health risk from these background exposures.
Dr. Elizabeth M. Whelan is president of the American Council on Science and Health, a nonprofit, consumer education organization dedicated to providing the public with mainstream scientific information on issues related to food, nutrition, chemicals, pharmaceuticals, lifestyle, the environment and health.